chapter 10: percents box 1 rules for manipulating percents 1.to convert a percent to its decimal...
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Chapter 10: PercentsBox 1
Rules for Manipulating Percents
1.To convert a percent to its decimal equivalent move the decimal point two places to the left.examples: 10% = 0.10 15% = 0.15 0.1% = 0.001
2. To change a decimal to a percent, move the decimal point two places to the right and add a % sign.examples: 0.10 = 10% 0.87 = 87% 1 = 100%
Chapter 10: PercentsBox 1
Rules for Manipulating Percents (continued)
3.To change a percent to a fraction, write the percent as a fraction with a denominator of 100.
examples: 30% = 30/100
1.5% = 1.5/100 100% = 100/100 = 1
Chapter 10: PercentsBox 1
Rules for Manipulating Percents (continued)
4. To change a fraction to a percent:Strategy 1: Use the logic of proportions
Change 50/75 to a percent
a. Set the problem up as a proportion equation
5010075
?=
Chapter 10: PercentsBox 1
Rules for Manipulating Percents (continued)
4. To change a fraction to a percent:Strategy 1: Use the logic of proportions
b. Cross multiply and divide
? = 66.66….. so 50/75 ≈ 66.67%
Chapter 10: PercentsBox 1
Rules for Manipulating Percents (continued)
4. To change a fraction to a percent:Strategy 2: Convert the fraction to its decimal equivalent and then move the decimal two places to the right and add a % sign.
a.Change the fraction to a decimal: 50/75 ≈ 0.6667
b. Change the decimal to a percent: 0.6667 ≈ 66.67%
Chapter 10: PercentsBox 1
Rules for Manipulating Percents (continued)
5. To find a percentage of a particular number convert the percent to its decimal equivalent and multiply the decimal times the number of interest.
Example: to find 45% of 900a.Convert the percent to a decimal:
45% = 0.45
b. Multiply the decimal times the number of interest: 0.45 X 900 = 405
Chapter 10: PercentsAn Application of Percents: Percent Error of a
Micropipette
first, place an empty microcentrifuge tube on an analytical balance and push the “zero” or “tare” button
emptymicrofuge tube
“zero” button
Chapter 10: PercentsAn Application of Percents: Percent Error of a
Micropipette
look on thumb plunger for range
range should be 100-1000 µlon plunger
Chapter 10: PercentsAn Application of Percents: Percent Error of a
Micropipette
set to 500 µl by turning plunger
install a blue disposable tip
Chapter 10: PercentsAn Application of Percents: Percent Error of a
Micropipette
press plunger to first stop(not all the way down!)
insert tip just beneath surface of liquid
Chapter 10: PercentsAn Application of Percents: Percent Error of a
Micropipette
slowly let plunger go all theway up to bring up liquid
don’t insert tip too deep! very amateur!
Chapter 10: PercentsAn Application of Percents: Percent Error of a
Micropipette
weigh the water in the tared microfuge tube
place tip in tared microfuge tube and slowly push plunger all the way down to second stop
Chapter 10: PercentsAn Application of Percents: Percent Error of a
Micropipette
% Error = X 100%true value – average measured value
true value
Do the procedure at least three times and calculate the average weight. This value will go here.
500 mg (0.5000 g) is the true value
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